Electronic device manufacturers strive to produce a rich interface for users. Conventional devices utilize visual and auditory cues to provide feedback to a user. In some interface devices, kinesthetic feedback (such as active and resistive force feedback), and/or tactile feedback (such as vibration, texture, and heat), is also provided to the user, more generally known collectively as “haptic feedback.” Haptic feedback can provide cues that enhance and simplify the user interface.
A device may incorporate a variety of technologies for providing haptic feedback, comprising both active and resistive devices. Active haptic feedback devices, comprising, for example, devices incorporating motors, generally add energy to a system; resistive devices, such as devices incorporating brakes, generally remove energy from the system.
Conventional resistive actuators may utilize, for example, magnetic particle brakes, magnetorheologic or electrorheologic brakes, or magnetic (non-friction) brakes. Conventional magnetic particle brakes utilize a powder comprising particles of a magnetic material. When a current is applied, the particles line up. Rheologic fluid brakes utilize a fluid that changes viscosity when a current is applied. A magnetic brake generates a magnetic field, and when a piece of metal passes through the magnetic field, an anti-current is generated, causing a resistance to movement of the metal.